1. Field of the Invention
The present invention relates generally to a sound reproducing apparatus such as a tape recorder and, more specifically, to a playback apparatus capable of performing a pitch conversion of an audio signal reproduced at a speed other than the speed at which it was recorded.
2. Description of the Background
In electronic appliances, for instance, tape recorders and tape players, not only is the rotation frequency or number of revolutions of the motor controlled to drive the magnetic tape at the rated tape speed, but the rotation frequency of the motor also can be varied in response to a variable tape speed operation performed by the user.
Furthermore, in some other electronic appliances there is provided a pitch or frequency converting process that is carried out with respect to the reproduced audio signal from the magnetic tape and the like in accordance with a pitch converting amount provided by the user, thereby increasing or decreasing musical intervals, that is, the pitch of the sounds, in the reproduced sound signal.
On the other hand, when the tape drive speed is changed from that at which the sounds were recorded, the pitch of the sounds being reproduced is also changed. Thus, there is the great possibility that one can hardly listen to and understand such reproduced sounds whose pitch is varied. As a consequence, it would be preferable that the above-described pitch conversion is performed to obtain such sounds having easy listening musical intervals, even during high-speed reproduction or low-speed reproduction. For instance, in the case of a tape on which a conference or business meeting has been recorded, when this tape is reproduced or played back at high speed the musical intervals of the conversational voices becomes much higher than normal, so that the contents of the recorded voices cannot be easily grasped. To the contrary, when the pitch conversion of the voice output is performed in such a manner that the musical interval of this voice output is lowered, everyone can listen to the reproduced voice with easy listening musical intervals, for example, with the musical interval at the rated tape drive speed.
At this time, the pitch converting amount is not manually controlled by the user, but a preselected pitch converting amount is automatically set in response to changes in the amount of the tape drive speed. Even when the user changes the tape drive speed, useful appliances could be realized if such sounds having the musical intervals obtained during rated tape drive speed are reproduced as the output.
In order that a predetermined pitch converting amount is automatically set in response to the amount of change of the tape drive speed, all previously proposed systems require a mechanism capable of detecting the tape drive speed. For example, a rotation frequency detecting mechanism such as a frequency generator (FG) is mounted to the motor that provides the tape drive, and a pitch control signal for setting the pitch converting amount in response to an output of this rotation frequency detecting mechanism is produced. To detect the position of the slider of a variable resistor used in a motor servo circuit to control the tape drive speed, a detecting variable resistor is provided which is mechanically coupled to the speed control variable resistor, and then a pitch control signal is produced based on the resistance value of this detecting variable resistor.
Since such a detecting mechanism is required when a predetermined pitch converting amount is automatically set in response to the change amount of the tape drive speed, there are disadvantages in view of manufacturing cost and package spacing.